CLDN18 and gastric neoplasm: For example, although previous studies reported that mice lacking the stomach isoform of claudin-18 showed increased paracellular permeability, which accounted for the development of inflammation and gastric tumors, the findings of a recent study suggest that claudin-18 KO has no effect on paracellular permeability and rather affects anion permeability; these effects may be secondary to transcellular anion transporter expression/function changes in the absence of claudin-18 (34, 126, 127).